Road Safety Treatments For Reduction Of Rear-End Crashes On High-Speed Rural Roads

Question:

Develop a Mechanism for Cost-Effective Road Safety Treatments that will reduce rear-end crash Type Risk Exposure on High-Speed Rural South Australian roads with a Posted Speed limit 100 km/hr or greater.

The current chapter of literature review provides substantive findings, methodological and theoretical contribution to the road safety treatments that will contribute to reduction of rear-end crash risk on the South Australian high-speed rural roads having a speed limit of 100 km/her or higher. It provides a brief review of the Australian and NZ jurisdictions of road. A conceptual framework has been provided to outline the relationship between dependent and independent variables of this research. The Australian guidelines have been revised for identifying best practices in prevention of rear crashes detecting adequate risk factors focusing on Netherlands, UK, Germany and Sweden. Traditional treatment measures such as channelized right turn, pavement widening besides innovative and low order treatments like signage, increased sight lines and line markings are also provided. Crash data as well as traffic volumes are collated and analyzed finally developing rating tools to priorities locations for the research. 

Figure 1: Conceptual framework

(Source: Created by the author)

The green colored step is the gap of literature that is the cost effective solution.

 Rear-end crash is the most common type of crash found in the world with approximately 83.7% of the crashes in metropolitan areas, 10.5% in city areas and 5.8% in country region (Chen 2015). Analyses on crash timings highlights that rear-end crashes are more frequent over other crashes. Approximately two fifth of the CTP insurance reports claims are regarding rear end crash in South Australia that amounts to around one –fourth of the total CTP cost. Factors that are considered for preventing rear-end crashes in South Australian rural roads with speed limits over 100 kmph varies from place to place including limiting the speed limit beyond 100 kmph to a certain level, using traditional methods like using speed breakers and widening of roads, use of reflective road indicators and coarse wearing coarse on road surface.  

Figure 2: Average annual number of rural rear-end casualty crashes for each jurisdiction by severity (2006–10 inclusive)

(Source: Olinepublications.austroads.com.au 2017)

Germany

Road safety treatments taken into consideration for avoiding rear end-collisions include clearing up of stationary vehicles present at turnings of the road. In Germany, skid resistance is used as a technique for road safety treatment with adequate resurfacing at road sites.

UK

According to Beck (2014), collision avoidance systems used in the United Kingdom provides warning to the driver regarding a slowly moving vehicle ahead.

Sweden

Vehicle based countermeasures like conspicuity of rear vehicles through application of retro-reflective rear vehicle materials are also extensively used in Sweden. 2+2 road types are usually built in Sweden as a dual carriageway in which the road is separated by a steel barrier cable.

Hard shoulders are not provided in these roads and hence it cannot be designated as a motorway however, there are variants in Swedish lanes such as the 3.25m wide lanes. These roads are effective to prevent rear end crashes as junctions are provided at roundabout grades, Moreover vehicles are free to move on a dual carriageway each in opposite direction thus preventing any rear-end crash.   

Prevention of Rear-End Crashes in Australia and NZ

Netherlands

Netherland have adopted a radar system in vehicles that detect any rapidly moving or slowly progressing vehicles in the vicinity providing warnings to the driver regarding it.   

Rear end car crashes includes numerous risk factors such as the whiplash injuries that cause death of personnel especially at peak hour of traffic. Presence of intersection increases the risk potentials especially for the right turning vehicles. Parked vehicle at side of road also contributes to increased rear end accidents to about 56% in UK (Biqiang 2016).

Figure 3: Statistics of rear end crashes in UK rural roads

(Source: Ukroads 2017)

Loss of control is the root cause for fatal accidents on 38% rural roads and 30% motorways respectively. Higher speed and winding nature of rural roads also causes such accidents. Bendy, narrow rural roads also causes rear crashes at junctions, while overtaking, failure in negotiating bends.

Other risk factors associated to rear end crashes studied in Sweden are found to be inadequate attention in drivers, improper driving conditions like alcoholic or drug use condition driving.  Inattention of drivers causes distraction of drivers from usage of mobile phones, headway maintenance also causes drivers to get distracted and crash on rear ends of front car. Age of the driver if below 26 and above 75 are most likely considered to cause a rear crash. Males are found to be more susceptible to rear end crash besides alcohol content in blood. According to South Australian rural road scenario, intersections have high chances of rear crash, geometry of road, density of traffic; work zones and lighting are the major factors contributing to rear crash in rural roads of South Australia. 

Weng (2014) stated that tailgating is another major risk associated to rear crash as driving too close to a vehicle without sufficient distance between the successive vehicles might increase chances of collision. Different factors including weather, vehicle speed, visibility and numerous conditions for road leads to potential increase of risk through tailgating. When a vehicle tailgates, and suddenly the former vehicle applies brake, rear crash occurs and hence tailgating at South Australian at a posted speed limit of 100 kmph or more is a risk.      

Appropriate treatment measures found in prevention of rear-end car crashes are classified as traditional infrastructure treatments, low order treatments and innovative treatments.

Figure 4: Appropriate measures of treatment

(Source: Created by the author)

Traditional infrastructural treatments according to Austroads design codes include skid resistance treatments for higher wet to dry crash weather through analysis of slip speed, slip ratio, water film thickness, test tyre, temperature and equipments of measurement through harmonization and correlation. Road widening is another technique used in Australia for ensuring reduction of rear crashes that includes road geometric design and widening. That is based on table T3.1 widening on curves for a radius of 180 m curve, single unit bus or truck should have a total widening of 0.50, 180 for prime mover and trailer, 0.25 for B-double and 0.48 for type 1 road train (Harland 2016).

Road Safety Treatments in Netherlands, UK, Germany, and Sweden

Figure 5: Typical cross-section of a road in Australia

(Source: Lao 2014)

Channelized right turn helps in better traffic control at signalized intersections avoiding conflicts and rear-ends collisions additionally adding pedestrian safety. Li et al. (2014) stated that prevention of rear crash is prevented from local and state guidelines in terms of channelized right turn lanes helps in improving pedestrian safety, vehicular safety to approximately 55% and rear crashes by about 25%.         

Although Austroads do not recommend innovative treatments however, few of the innovations include proximity and accident warnings that have been beneficial in prevention of rear crashes. Proximity sensors help vehicles in detecting high speed approaching vehicles and slowing vehicles in front so that braking time is anticipated and possibility of rear crash is reduced. Latest technological innovation includes smart GPS through in built autopilot system that gets prior notification of traffic and hence prepares its track course that prevents any possibilities of accident. Vision zero program in Sweden refers to the setting up of speed limits suitable to a particular area through dynamic messaging through speed warning sign as well as variable messaging signs. Speed indicator displays (SIDs) to rural roads also help in anticipating any potential rear crash due to approaching vehicles from behind.

Use of traffic lights with proper red, amber and green cycle timing depending on the traffic density of the area also allows vehicles to prevent any unwanted events. Moreover, line marking is used for providing a guideline for preventing vehicles to go out of track and cause any accidents.

Figure 6: Line of sight

(Source: Liu 2016)

Increased line of sight provides the traffic drivers to get a better vision on road and thus see any vehicles moving at the opposite end of line of sight. Braking time refers to the total effective time taken for the brakes to be applied from perception until actual stopping of the car. If line of sight is increased, car drivers will get ample time to use brakes and thus prevent unavoidable circumstances of rear crash. Reflective raised pavement markers are important in getting a clear road vision and thus help the drivers to get an image of the road ahead preventing any detrimental rear crash.    

Traffic volumes of a place help in analyzing the potential traffic congestion of that intersection  and assess the traffic density so that the widening of the road can be determined and possible traffic congestion can be reduced. Moreover, crash data of a place when analyzed helps in calculating the possible anticipated right channelization need and requirement for reflective raised pavement markers. As per Metzger (2015), the analysis throws light on around 88% of the rear crashes that occurs and necessary steps that are required for avoiding the accident.

Collation and analysis of crash data at intersection of high-speed rural roads shows that rear-end crashes occurs more frequently at higher speed sites and at around 32% in low speed and 42% high speed at crossings where no turns are allowed (Mitchell 2015). Right turning points also faces accidents at 23% low speed and 45% high-speed. Parenteau (2014) stated that rear end crashes occurs more frequently about 27% at high speed and 12% at low speed. Collation and analysis of crash data is usually done over a certain period and dividing the sites into categories AADT, which are low, moderate, and high volume roads. Analysis of crash data shows around 71% of vehicle crash occurs in speed zones more than 76 Kmph. Intermediate and large crash of cars occurred at higher speed of more than 75 Kmph in rural areas (Monash.edu 2004).

Risk Factors Associated with Rear-End Crashes

Risk factors at intersection identified that are associated to rear-end crashes includes age of driver, speed zone, traffic control type, time of the day, type of crash and usage for seat belt. It has been seen that without usage of seat belt a whiplash effect is created that makes the driver face a serious accident leading to death. As per Viano (2015), age of driver also comes into play with young drivers more susceptible to accidents due to immature decisions as well as time of day with more accidents occurring at night. Finally, traffic control type also decides the intensity of accidents occurring at a location as insufficient traffic control leads to uncontrollable situation.

Scoring system using sensitivity analysis

Rear crash accidents being major issue in Australian rural highways is commonly seen in trucks, which are overloaded. Identification of vehicle speed is another factor that understands the dynamics of vehicle and influencing factors such as rolling coefficient of resistance, gradient of road surface and coefficient of air resistance on the vehicle speed (Sahraei 2014). Sensitivity analysis shows that rolling resistance coefficient, gradient of road surface influences vehicle speed with a slight air resistant coefficient. Therefore, in a sensitivity analysis, besides speed of vehicle, air coefficient of resistance is taken into consideration. 

Sensitivity analysis shows that capital costs to be nearly 20%, VOC to be 20%, TTC to be around 40%, accidental cost to be 20% and exclude all private travel time costs. Best estimate assumption has been considered which is around AU$50 million of costs, AU$40 million of capital cost, AU$10 million for operating costs, AU$ 70 million for benefit cost and AU$40 million for TTC savings. It is also estimated to be AU$ 1 million for VOC savings, accidental savings to be around AU$10 million, first year benefits to be around AU$2 million at a discounting rate of 4%. The assumptions made by the sensitivity analysis of The Transport and Main Road Cost Benefit Analysis involves BCR to be 1.4, NPV to be around AU$ 20 million and FYRR to be 4% (Tmr.qld.gov.au 2017). For prioritizing intersections, sensitivity analysis is usually used that leads to placing of the important factors against the crash, sight distance and AADT in order to ensure the sight with crash location does not get any kind of high priority importance that might lead to serious consequences populating the tops. Using sensitivity analysis usually, the intersections are prioritized and practitioners of traffic uses proactive basis for selecting top intersections.     

Gap of literature

According to Beck (2014), it has been found that major factors for rear crash accidents in Australia happens due to improper driving skills, improper adherence to traffic rules and improper infrastructure of road. Biqiang (2016) stated that often accidents occurs frequently at intersections on right turns and happens due to improper line of sight, skid resistance and other factors like age of driver. Hence, the gap of the literature has been found which is the relationship of road safety treatments that are cost effective reducing exposure to high-speed rural roads of Australia.

Treatment Measures for Rear-End Crashes

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